Transparent closure



May 8,1945. D. w. DUNIPACE TRANSPARENT CLOSURE Filed Dec. 7'-, 1942 maman-*0cm abCS r T izan/IAL :inventor Y DONA/ 0 WDM/PACE,

' attorneg Mm-#a Mer 8i,

UNHE'D STATES PTENT- OFFICE l c 2315.352 I TRANSPARENT CLOSUBE 'nomia w. Denisse, remsbmg, om, mmmto Libbey-OwensFord Glass Company, Toledo,L

Ohio, a corporation! o! h10 Application December 7, 1942, Serial No. 468,058

(c1. ss-r) A "GClaima My invention relatesv to curved or bent transparent closures and to the shape or design of such closures to obtain certain predetermined optical advantages.

In the use of curved or bent closures or windows for ordinary glazing purposes, such as .in homes, forstore fronts, and the like, a deviation in the line of sight is not particularly objectionable. However, in the glazing of observationstations,

s such as in airplanes, combat vessels, mobile combat units, shore batteries. etc., and especially in those windows .or panels through which sighting observations are performed, a relatively small amount of deviation in the line of sight may result .111 the presence of 'an abnormal sighting error. For example, tests' conducted upon several windows of a given design, having a cylindrical area Joined tangentially with a at. area, have show n that sighting errors occur 'through approximately the same parts of the several windows tested in both %v inch and Vs inch thicknesses. The sight- I have'discovered, however, that it is possible to vary one of these factors in such a way as to compensate for the eiIect of the other and thus produce a curvature so related to the changing angle of incidence of the linev of sight through the K window that a maximum amount of change. in

f range except at the extreme limits or opposite ing errors also corresponded roughly in value for all of the windows. It was found `that the amount by which the line of sight was deviated varied from about 0.0 to about 14 mils, varying somewhat from one window to another. When it is recogniaed that 14 mils corresponds to 42 feet at 1,000 yards, the possibilities oi error resulting from the use of such a window for gun .sighting becomes apparent. The variation of deviation depends, of course, on the shape of the window and would therefore vary as between different types of curva- The gun sight commonly used in airplanes is ordinarily mounted to swing about a horizontal axis through approximately a 90 arc or, in other words, between a horizontal position and a verhcal position. The sighting errorin the particular type of window referred to above was found to lncrease in magnitude as the line of sight was elevated from the horizontal vsighting position reaching a maximum value at about v20 degrees elevation and then falling oi rapidly to a low value at 35 degrees. Above 35 degrees elevation the sighting error remained relatively slight.

, The deviation' inthe line of sight depends on both the curvature ofthe glass at any-given point andthe angle of incidence at 'whichl observations` are made.4 If both the curvature and angle of incidence could be held constant, then the deviaends thereof. In other words, While there is adeviation resulting from an elliptical bend, the change in deviation is quite small, and actually .this small variation occurs at the ends of the or shaped as to produce a-'minimum variation of deviation throughout the sighting range.

With reference to the drawing, the two foci or Y` focal points of the-ellipse are indicated atf and f. with the gun sight and more particularly the point of observation being located at the focus f. 4Upon tion would also be constant. In general, this is a practical impossibility since, while it is possible to maintain either ofthese factors constant, it is not pomble to maintain both of them constant at the same time.

operation of the gun sight through a arc, the line of sight will pass through 'the glass window p between the lower linut t to the upper limit t'.

After irst locating the focuscf, which is determined .by the point of observation, the locating of the focus f is determined inthe following manner: Focus'f' is located at a distance froml t' 'equal to the distance between t andf and at a distance from t corresponding-to the distance between t and f. 'I'he major axis of the ellipsehas a length of 2a equal to the sum ofthe distancesY Afrom f to t and f to t or the sum of the distances from f to t' and f to t', The distance between the two foci is 2c and the length of the'minor axis is 2b which is equal to the square root of the diierence between the squares ofthe maior axis and the interfocal distance f to f'. Thus, the

ellipse is oriented so that its 'majoraxis is parallel to the line passing through t andt' and has animatav Y vation, said closure comprising a transparent point locatedat the observationposition-and the .Y 'panel having a curvature along a path of observation therethrough approximating a portion of an ellipse passing. lthrough two predetermined points in said path, one located on the line of sight adjacent one limiting position and the other located on the line of sight adjacent its opposite limiting position, said ellipse having one focal point )located at the observation position and the other focal po/int located at a distance from said rst mentioned predetermined point equal to the distance between the opposite -predetermined point and the rst focal point and at a distance ,from said opposite predetermined point corresponding to the Adistance between the first-mentioned point and the first focal point, and said ellipse being so oriented that its major axis is parallel to a line passing through said two predetermined'points and that said observation position is located at the focus nearest the first-mentioned predetermined point.

5. A transparent, laminated closure for a vethe distance between the opposite predetermined hicle constituting/a window through which observations can be performed from a predetermined position within the vehicle with 'a substantially panel of substantillyvuniform thickness havother focal point located at a distance from said first-mentioned predetermined point equal to point and the ilrst focal point and at a distance from said opposite predeterminednpoint corresponding to vthe distance between the` Afirst- Amentioned predetermined point and .the vfirst focal point, an`d said ellipse being so oriented that its .major is parallel toa line passing through said two predetermined points and that said 'observation position is located vat the focus nearest the first-mentioned predetermined point.

6. In a vehicle having a sight opening, a curved transparent -closure therefor' constituting a window through which observations canv be .per-

lformed from aaposition normally occupied' by an occupant'of thevehicle witlra constant deviation of the line of sight from said position throughout the effectivel range of observation, said :closure comprising a transparent panelof 'substantially' line ofvsight from said observation position increases at a rate calculated toevercome the variation in deviation in the line of sight as it ing a curvature along a path of observation therethrough approximating a portion of an elcated on the line of sight adjacent` its:` opposite` limiting position, said rellipse having one localH passes through said panel and approximating a v portion of an ellipse, said ellipserbeing so oriented as to pass through two points determined by the intersection of the line of sight' with the op- Aposit@ limits or said sight opening and having hicle. f

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